Centrifugal mercury switch



Jan. 11, 1955 A, wl GARDES 2,699,475

CENTRIFUGAL MERCURY SWITCH Filed Nov. 6, 1955 United States Patent O M CENTRIFUGAL MERCURY SWITCH Alfred W. Gardes, Detroit, Mich., assignor to Houdaille- Hershey Corporation, Highland Park, Mich., a corporation of Michigan Application November 6, 1953, Serial No. 390,610

4 Claims. (Cl. 200--80) The present invention relates to speed-responsive switches, and more particularly, contemplates the provision of a highly eicient speed-responsive switch utilizing an electrically conductive liquid under the inuence of centrifugal force.

I am, of course, aware of prior art attempts to obtain a highly accurate speed-responsive switch structure for use in automotive and similar controls. While very many satisfactory switches have been provided by the prior art, these switches have, to my knowledge, all been very complex in construction, and hence relatively expensive. Further, mechanical centrifugal or other speed-responsive switches having snap actions, centrifugal weights, or other mechanical linkages associated therewith, have a tebndency to be very critical and unable to stand constant a use.

The speed-responsive switch structure of the present invention has provided a switch which is both accurate and extremely simple. By utilizing a pool of electrically conductive uid in combination with a pair of separated contacts and by displacing the lluid into overlapping or bridging contact with the contacts upon the attainment of a predetermined speed, I have been enabled to provide a speed-responsive switch having only a single moving part, which is Very accurate, and which has substantially innite life, even under unusually severe loads or abuse.

It is therefore an object of the present invention to provide a centrifugal switch in which a vaned rotor is mounted in a pool of electrically conductive uid whereby rotation of the rotor will displace the fluid into overlapping contact with a pair of normally opened electrical switch contacts.

Another object of the present .invention is to provide a novel centrifugal switch capable of operation in substantially any position.

Still another object of the present invention is to provide a speed-responsive switch having only a single moving part.

Still a further object of the present invention is to provide a centrifugal switch in which substantially no mechanical wear occurs.

Still other objects will at once become apparent to those skilled in the art from a consideration of the attached drawing in which two modifications of the present invention are shown by way of illustration only.

On the drawings:

Figure 1 is a side elevational view in cross-section of the novel centrifugal switch of the present invention;

Figure 2 is a cross-sectional view of the switch taken along the line II-II of Figure 1; and

Figure 3 is a side elevational view of a modified form of the invention.

As shown on the drawings:

The switch of the present invention comprises a fixed outer housing, generally indicated at 10, mounted for rigid support on a casing 11 of conventional form which is associated with apparatus having a part the speed of which is to be sensed. A shaft 12 is supported in the casing 11 by means of a suitable bearing 13 and is rotated by gearing or other means, not shown, in response to rotation of the part being sensed.

In practice, for example, the shaft 12 could be directly driven by gearing from an automobile transmission to sense the speed of rotation of parts thereof for purposes of automatically shifting gears. Another example of a possible drive for the shaft 12 would be gears associated Patented Jan. 11, 1955 with an automobile speedometer whereby the shaft 12 would rotate in response to vehicle speed for purposes of energizing automatic vehicle overdrive units or other similar vehicle speed-responsive apparatus. It is to be understood, however, that the shaft 12 may be rotated by any means whatever, automotive or otherwise, and that the apparatus controlled by the switch of the present invention forms no part whatever of this invention.

The rotating shaft 12 is drivingly connected to a rotor 14, having vanes 15, by means of conventional at spline 16. The rotor 14 is maintained in axial position relative to the housing 10 by means of a bearing support dimple 17.

The housing 10 is provided with internal threads 18 that cooperate with external threads 19 on an intermediate support 20 which is in turn iixedly secured to the casing 11 by threads 21. It will be noted that the outside diameter of the support 20 is slightly larger than the maximum diameter of the blades 15 of the rotor 14, thereby permitting assembly of the housing 10 by consecutively assembling the support 20 to the casing 11, positioning the rotor 14 on the shaft 12 in driving relation thereto and. subsequently threading the housing 10 onto the support 20.

A pair of annular electrical contacts 22 and 23 are embedded in the walls ofthe housing 10 connected into any conventional electric circuit by means of the respective conductors 24 and 25 securely fastened to the posts 26 and 27 by means of the nuts 28 and 29.

In order to prevent short-circuiting of the contacts 22 and 23, it is, of course, contemplated that the material from which the housing 10 is manufactured will be of a dielectric nature. For this purpose, it is preferred that a hard, impact-resistant, plastic material be utilized, since such materials have sucient inherent resiliency to prevent fracture upon impact from stones, or other similar flying articles, or shocks. Likewise, the rotor 14 and its blades 15 are preferably constructed of a dielectric plastic material, although it is to be understood that the rotor 14 and its blades 15 may be of a conducting material if, in the alternative, provision is made to electrically insulate the rotor 14 from the metallic shaft 12, thereby preventingdgounding of the circuit formed by the conductors 24 an 5.

During assembly of the switch, as above described, a pool of electrically conductive liquid, such as mercury 30, is placed in the bottom of the housing 10. This pool is of suicient depth to cover a portion of the walls of the rotors 15 but is of insufiicient depth to cover both of the contacts 22 and 23. Thus, in the normal condition, in which the shaft 12 is not rotating, the circuit including the contacts 22 and 23 will be in the opened position and no current will be permitted to ilow.

In operation, when the shaft 12 begins to rotate, the rotor vanes 15 will impart energy to the liquid 30 forcing the liquid to position itself against the cylindrical inner wall 10a of the housing 10. As the speed of the shaft 12 increases, the force imparted to the fluid 30 will likewise increase and the fluid will tend to assume a position substantially out of contact with the blades 15 along the peripheral wall 10a. Upon the increase in speed of the shaft 12 to a predetermined point, the centrifugal force generated by the rotating vanes 15 will cause the tuid 30 to spread out on the wall 10a, thereby moving upwardly until it contacts the annular contact 22 ,thereby bridging the contacts 22 and 23 and closing the electrical circuit.

It will, of course, be understood that the exact speed at which the contacts 22 and 23 are bridged will depend upon the amount of conducting fluid 30, the distance between the outer periphery of the vanes 15 and the inner wall 10a of the housing, and the angle of the side wall 10a relative to the axis of shaft 12. Thus, as the amount of mercury of similar electrically conducting uid 30 is increased, the speed at which the contacts 22 and 23 will be bridged will be reduced, and likewise, as the maximum diameter of the blades 15 approaches the inside diameter of the wall 10a, the speed at which the contacts 22 and 23 will be bridged will be reduced. Again, if the walls 10a converge toward the bottom the bridging speed will be lower than if the walls diverged toward the bottom.

In this respect, the cylindrical arrangement shown in Figs. 1 and 2 has provided a very satisfactory degree of accuracy.

While the above-described centrifugal fluid switch may be operated satisfactorily in a position which is substantially vertical, or in any position of sufficient inclination from the horizontal so that the rings 22 and 23 are not bridged by the pool 30 during periods of no shaft rotation, it is apparent that the annular contact structure utilized in the embodiment shown in Figures 1 and 2 cannot be satisfactorily employed where the speed-sensing shaft 12 is forced to lie in a substantially horizontal position. A modified switch structure is therefore provided for horizontal operation and may take the form shown in Figure 3. As will be apparent from a consideration of the modified form, however, the modified form may be operated in substantially any position, horizontal or vertical, and may in some cases be found convenient as a universal speed-responsive switch.

As is shown in Figure 3, the modified switch comprises a housing 110 constructed of a dielectric material and threadedly mounted on the support 120 which is in turn securedly threaded to the casing 111 through conventional threads 121. Contacts 122 and 123 are permanently embedded in the dielectric material of the housing 110 and are electrically connected to the conductors 24 and 25 by means of posts 126, 127 and fasteners 128 and 129, respectively.

The rotor 114 is substantially the same as that shown in Figures l and 2, with the exception that the blades 115 carried thereby are tapered to conform substantially to the frusto-conical wall 110a of the housing. The shaft 112 like that shown in Figure 1, is mounted in the casing 111 by means of a conventional bearing bushing 113 and is secured to the rotor through a flat spline 116 as described above relative to the rst embodiment.

Since the entire switch structure is positioned in a substantially horizontal position as viewed in Figure 3, the pool of mercury 130 takes a position substantially as shown in Figure 3 and in contact only with the portion of the rotor blades 115 having the greatest radius. It will be appreciated that upon rotation of the shaft 112, the mercury 131) will be thrown radially outwardly of the shaft 112, initially positioning itself at the point of greatest radius of the blades 115. As the speed of rotation of the shaft 112 increases, the mercury spreads out on the frusto-conical wall ln, gradually working toward the contact 122. Upon the attainment of a predetermined critical speed, the mercury film extends in a frusto-conical film reaching from the point of greatest radius 110b to a point in contact with the contact 122 and the electrical circuit is completed.

As may be surmised, the clearance between the rotor blades 115 and the frusto-conical surface 1100 is very important in the embodiment shown in Figure 3 since movement of the film of mercury or other electrical conducting iluid along the frusto-conical surface 110a in a direction of decreasing radius is accomplished as a result of the fluids attempt to position itself immediately outside the path of the rotating blades 115. Of course, the higher the speed of rotation of the shaft 112, the more of the mercury will be flung outside the path of the vanes 115, thereby filling the space between the vanes and the wall l10n.

It will be apparent that the structure shown in Figure 3 may be operated in a vertical direction in the manner shown relative to the modification in Figure 1. In the vertical position, the pool of mercury would, of course, assume a position substantially the same as that shown in Figure 1 and the bridge between contacts 122 and 123 would occur upon rotation of the rotor 114 to a sufficient extent to cause the mercury to climb the frusto-conical wall 1I0a from the point adjacent contact 122 to the altitude of the contact 123. In all other positions, the switch will operate substantially in the manner as described relative to its horizontal position.

As may be seen from the above description, I have provided a switch with but one wiring part. It has been found in most cases that the conductive fluid 30 will provide the necessary lubrication to prevent wear between the parts 10 and 14. In any case, however, it is contemplated that lubrication be supplied by the fluid 30 and lubricating additives may be included to the fluid where found desirable.

It will thus be apparent that the present invention has provided a novel and extremely simple centrifugal, speedresponsive switch which is capable of heavy duty use with an absolute minimum of wear. While, two modified forms of the present invention have been illustrated, it is to be understood that other variations and modifications may be made in the structure illustrated without departing from the novel concepts of the present invention.

I claim as my invention:

l. A horizontally operable centrifugal switch comprising a substantially frusto-conical housing constructed of a dielectric material and having its axis substantially horizontal, a vaned rotor mounted for rotation around the axis of said housing and having a plurality of tapered vanes conforming substantially to the frusto-conical wall of said housing, a pool of electrically conductive fluid in said housing in contact with said vanes and normally covering a contact positioned at the bottom point of said housing at its point of greatest radius, and a second contact positioned on the top of said housing adjacent its point of minimum radius, and means for rotating said rotor.

2. A universally mountable centrifugal switch comprising a tapered housing having a vaned rotor mounted for rotation therein, said rotor having vanes extending into substantially conforming relation with the taper of said housing, a pair of contacts positioned in said housing at points substantially diametrically opposite from each other and displaced along the axis of said rotor, and a pool of electrically conductive fluid in said housing and positioned, during inactivity of said rotor, in the path of rotation of said rotor vanes.

3. A switch structure in accordance with claim 2 wherein said rotor and housing are provided with cooperating interengaging bearing and alignment means lubricated by said fluid.

4. A switch structure in accordance with claim 2 wherein said housing comprises a frusto-conical cup internally threaded at its large end and having the rotor retained therein by an externally threaded support having an aperture therein for the passage of means for supporting and rotating said rotor.

References Cited in the le of this patent UNITED STATES PATENTS Re. 8.102 Weston Feb. 26, 1878 FOREIGN PATENTS 256,448 Germany Dec. 3, 1911 

